The Promise of Thermochemical Conversion of Biomass to Biofuels
University of Nebraska Faculty Retreat: Energy Sciences Research
May 15, 2007
Robert C. BrownOffice of Biorenewables Programs
Iowa State University
Why thermochemical conversion?
Try this with enzymes.
Why is cellulose so difficult to enzymatically decompose?
• Starch is a storage polysaccharide designed by nature as a food reservoir
• Cellulose is structural polysaccharide designed by nature to resist degradation
Thermochemical conversion can produce more than just ethanol
Fuel Specific Gravity
LHV (MJ/kg)
Octane Number
CetaneNumber
Ethanol 0.794 27 109 -Biodiesel 0.886 37 - 55Methanol 0.796 20.1 109 -Butanol 0.81 36 96 - 105 -Mixed Alcohols ~0.80 27-36 96-109 -Fischer-Tropsch Diesel 0.770 43.9 - 74.6
Hydrogen 0.07 (liq) 120 >130 -
Methane 0.42 (liq) 49.5 >120 -Dimethyl Ether 0.66 (liq) 28.9 - >55Gasoline 0.72-0.78 43.5 91-100 -Diesel 0.85 45 - 37-56
Thermochemical Options
• Gasification
• Fast pyrolysis
• Hydrothermal processing
Gasification• Gasification - high temperature (750 –
1800 °C) conversion of solid, carbonaceous fuels into flammable gas mixtures– Carbon monoxide (CO), hydrogen (H2),
methane (CH4), nitrogen (N2), carbon dioxide (CO2), and smaller quantities of higher hydrocarbons
– Gas mixture called producer gas or syngas
• Gas production is endothermic– Requires either the simultaneous burning of
part of the fuel or the delivery of an external source of heat to drive the process
5 tpd biomass gasifier at BECON facility in Nevada, IA
Why Gasification?
Biomass
CO + H2
COMBUSTION CO2 + H2O
GASIFICATION WATER-GAS SHIFT
CATALYSIS/ BIOCATALSIS
H2 + CO2
Organic acidsAlcoholsEstersHydrocarbons
THERMAL POWER
FUEL CELLS
FUELS & CHEMICALS
Air
Steam
Updraft
Common Types of GasifiersDowndraft Entrained Flow
AshOxidant
BiomassProduct gas
Product gas + ash
Oxidant
Biomass
ThroatGrate
Product gas + fly ash
Freeboard
Fluid bed
Oxidant
Biomass
Feeder
Distributorplate
Fixed bed of
biomass
Fixed bed of
biomass
Slag
BiomassSteam and Oxygen
Product gas
Fluidized Bed
Gasification Efficiency
• Thermal efficiency - conversion of chemical energy of solid fuel to chemical energy and sensible heat of gaseous product– High temperature, high-pressure gasifiers: >95% – Typical biomass gasifiers: 70 - 90%
• Cold gas efficiency – conversion of chemical energy of solid fuel to chemical energy of gaseous product– Typical biomass gasifiers: 50-75%
Synthetic Fuels from SyngasProcess Products
Steam Reforming Hydrogen
Methanol synthesis
Methanol, acetic acid, ethanol, diethyl ether, olefins
Fischer TropschSynthesis
Synthetic diesel and gasoline
Alcohols from Syngas
Ethanol, mixed alcohols
Syngas Fermentation
Ethanol, esters, and other metabolic products
Biomass‐to‐Fuels Efficiencies (current technology)
References:1. A. McAloon, F. Taylor, W. Yee, K. Ibsen, and R. Wooley, “Determining the Cost of Producing Ethanol from Corn Starch and Lignocellulosic Feedstocks,” National Renewable Energy Laboratory Report, October 2000.2. C. N. Hamelinck, G. van Hooijdonk, and A. PC Faaij, “Ethanol from lignocellulosic biomass: techno-economic performance in short-, middle-, and long-term,” Biomass and Bioenergy. 22, 384-410, 20053. C. N. Hamelinck, and A. Faaij, “Future prospects for production of methanol and hydrogen from biomass,” Journal of Power Sources 111, 1-22, 2002.4. M. J.A. Tijmensen, A. P.C. Faaij, C. N. Hamelinck, and M. R.M. van Hardeveld, “Exploration of the possibilities for production of Fischer Tropsch liquids and power via biomass gasification,” Biomass and Bioenergy 23, 129-152, 2002.
Fuel Production EfficienciesGrain Ethanol1 38%Lignocellulosic Ethanol2 35%Methanol3 45%Hydrogen3 50%Fischer-Tropsch4 45%
*BPD – barrels per day **MMGPY – million gallons per year (gasoline equivalent) Note: Efficiencies do not account for byproduct value or power production although production costs do.
Thermochemical
Biochemical
Comparing Costs
References for Base Case Data:1. A. McAloon, F. Taylor, W. Yee, K. Ibsen, and R. Wooley, “Determining the Cost of Producing Ethanol from Corn Starch and Lignocellulosic Feedstocks,” National Renewable Energy Laboratory Report, October 2000.2. C. N. Hamelinck, G. van Hooijdonk, and A. PC Faaij, “Ethanol from lignocellulosic biomass: techno-economic performance in short-, middle-, and long-term,” Biomass and Bioenergy. 22, 384-410, 20053. C. N. Hamelinck, and A. Faaij, “Future prospects for production of methanol and hydrogen from biomass,” Journal of Power Sources 111, 1-22, 2002.4. M. J.A. Tijmensen, A. P.C. Faaij, C. N. Hamelinck, and M. R.M. van Hardeveld, “Exploration of the possibilities for production of Fischer Tropsch liquids and power via biomass gasification,” Biomass and Bioenergy 23, 129-152, 2002.
150 MMGPY* Capital Operating Feedstock Capacity (2005 basis) Cost Cost Cost
($/bpd)* ($/gal)Grain Ethanol1 13,000 1.11 $1.84/buLignocellulosic Ethanol2 76,000 1.76 $50/tonMethanol3 66,000 1.19 $50/tonHydrogen3 59,000 1.07 $50/tonFischer-Tropsch4 86,000 1.87 $50/ton
*BPD – barrels per day **MMGPY – million gallons per year (gasoline equivalent) Note: Operating costs include credit for byproduct utilization.
$3.00/bu$1.74/gal
Fast Pyrolysis
• Rapid thermal decomposition of organic compounds in the absence of oxygen to produce liquids, char, and gas– Small particles: 1 - 3 mm– Short residence times:
0.5 - 2 s– Moderate temperatures
(400-500 oC)– Rapid quenching at the
end of the process– Typical yields
Oil: 60 - 70%Char: 12 -15%Gas: 13 - 25%
Bio-OilSource: Piskorz, J., et al. In Pyrolysis Oils from Biomass, Soltes, E. J., Milne, T. A., Eds., ACS Symposium Series 376, 1988.
White Spruce
Poplar
Moisture content, wt% 7.0 3.3
Particle size, μm (max) 1000 590
Temperature 500 497
Apparent residence time 0.65 0.48
Product Yields, wt %, m.f.
Water 11.6 12.2
Gas 7.8 10.8
Bio-char 12.2 7.7
Bio-oil 66.5 65.7
Bio-oil composition, wt %, m.f.
Saccharides 3.3 2.4
Anhydrosugars 6.5 6.8
Aldehydes 10.1 14.0
Furans 0.35 --
Ketones 1.24 1.4
Alcohols 2.0 1.2
Carboxylic acids 11.0 8.5
Water-Soluble – Total Above 34.5 34.3
Pyrolytic Lignin 20.6 16.2
Unaccounted fraction 11.4 15.2
Pyrolysis liquid (bio-oil) from flash pyrolysis is a low viscosity, dark-brown fluid with up to 15 to 20% water
Bio-Oil • Advantages include:
– Liquid fuel– Decoupled conversion
processes– Easier to transport than biomass
or syngas• Disadvantages
– High oxygen and water content makes bio-oil inferior to petroleum-derived fuels
– Phase-separation and polymerization and corrosiveness make long-term storage difficult
Fundamentals of Fast Pyrolysis
• Multiple reaction pathways for pyrolysis of cellulose
Fast
Cellulose
Slow
Alkali-catalyzeddehydration
Levoglucosan
Hydroxyacetaldehyde
Char + water
Depolymerization O O
OH
OH
OH
O
OH
Several kinds of pyrolysis technology
Adapted from PYNE IEA Bioenergy http://www.pyne.co.uk
High
MA
RK
ET
AT
TR
AC
TIV
EN
ES
S
Low
Strong Average Weak
Ablative
Cyclonic
Rotating cone
Entrained flow
Fluid bed
Circulating fluid bedand transport reactor
Auger
TECHNOLOGY STRENGTH
Energy efficiency of bio-oil production
• Conversion to 75 wt-% bio-oil translates to energy efficiency of 70%
• If carbon used for energy source (process heat or slurried with liquid) then efficiency approaches 94%
Source: http://www.ensyn.com/info/23102000.htm
Synfuels from bio-oil: Hydrocracking• Directly converts biomass into liquid bio-oil (lignin,
carbohydrate derivatives, and water) and char• Bio-oil catalytically converted into hydrocarbon fuel
(green diesel)
Pyr
olyz
er Carbohydrate derived aqueous phase
Bio-Oil Recovery
Phase Separation
Steam Reformer
Hyd
rocr
acke
r
Fibrous biomass
Bio-oil vapor
Hydrogen
Green diesel
Cyclone
Lignin
Char
Synfuels from bio-oil: Gasification• Bio-oil and char slurried together to recover 90% of
the original biomass energy• Slurry transported to central processing site where it is
gasified in an entrained flow gasifier to syngas• Syngas is catalytic processed into F-T liquids
Pyr
olyz
er
Bio-Oil Recovery
Slurry Preparation
Pump
Ent
rain
ed F
low
G
asifi
er
Fibrous biomass
Bio-oil vapor
Slag
Cyclone
Bio-Oil
Char
Fisc
her T
rops
ch
Rea
ctor
Green Diesel
Co-Products• Gas (CO, H2, light hydrocarbons)
– Can be used to heat pyrolysis reactor
• Char: Several potential applications– Process heat– Activated carbon– Soil amendment– Carbon sequestration
Nature, Vol. 442, 10 Aug 2006
Agri-char: Soil amendment and carbon sequestration agent
Car
bon
Stor
ed (l
b/ac
re/y
r)
0200400600800
100012001400160018002000
Pyrolytic Char No-Till Switchgrass No-Till Corn Plow-Tilled Corn
Char from pyrolyzing one-half of corn stover
Greenhouse gases reduced by carbon storage in agricultural soils
Hydrothermal Processing (HTP)
• Processing in hot, compressed liquid water orsupercritical water
• Pressure and temperature determine products:– Carbohydrate from HTP: 200°C and 20 bar yields
carbohydrate that can be hydrolyzed to fermentable sugars
– Biocrude from HTP: 330°C and 150 bar yieldshydrocarbons suitable for production of diesel fuel
– Syngas from HTP: 600°C and 230 bar yields hydrogen, carbon monoxide, and methane
Carbohydrate from HTP
• Feedstock: Fibrous (cellulosic) biomass
• Conditions: 200 C; 20 bar in liquid water
• Typical products: Fractionated cellulose, lignin, and pentose (from hemicellulose)
• Applications: Pretreatment for more effective simultaneous saccharification and fermentation
Biocrude from HTPFeedstock: A variety of wet biomass
Conditions: 300 - 350 C; 120 - 180 bar for 5 - 20 minutes in liquid water
Products: 45 Biocrude (%w on feedstock, DAF basis)25 Gas (> 90% CO2)20 H2O10 dissolved organics (e.g., acetic acid, ethanol)
Properties: Biocrude is a heavy organic liquid, immiscible in water that solidifies at 80 C; H/C = 1.1; oxygen content 10 -18 %w; LHV 30 -35 MJ/kg
Efficiency: 70 - 90 %
Developers: Changing World Technologies (West Hampstead, NY), EnerTech Environmental Inc (Atlanta, GA), and Biofuel B.V. (Heemskerk, Netherlands), TNO (Netherlands).
Syngas from HTP
• Conditions: 600 - 650 C; 300 bar for 0.5 - 2 minutes in supercritical water
• Theoretical: 2 C6H2O6 + 7 H2O => 9 CO2 + 2 CH4 + CO + 15 H2
• Typical products:– H2 56 v%– CO 4 v%– CO2 33 v%– CH47 v%
• Applications: Syngas for Fischer-Tropsch reaction or other catalytic synthesis reactions
CO2
Cellulose Enzymes
Fermenter
Saccharification
Fibrous Crop
Pretreatment
Distillation
water
Lignin
C5 & C6 Sugars
Ethanol & other fermentation products
Hybrid biochemical/thermochemical biorefinery
Gasifier
SyngasGas Cleaning Catalytic Reactor
Biobased fuels
Air
CO2
Lignin gasified to CO and H2
Heat
Hybrid thermochemical/biochemical biorefinery – Syngas fermentation
Biomass SyngasGas Cleaning
Biobased fuels and chemicals
Air
CO2
Bioreactor
Gasifier
Syngas fermentation: Advantages & challenges
• Advantages compared to cellulose hydrolysis– Both carbohydrate and lignin converted to syngas– Less finicky about composition of feedstock
• Advantages compared to Fischer-Tropsch– Robust to inorganic contaminants– Opportunity to diversify products
• Challenges– Gas-liquid transfer is bottleneck – Some tarry products are fermentation inhibitors– Limited development of suitable microorganisms
Fermenter
FiberP
yrol
yzer
Anhydrosugar & other carbohydrate
Bio-Oil Recovery
Phase Separation
Detoxification
Lignin
Hot water extraction
Pentose
Fibe
r byp
rodu
ct Bio-oil vapor
Fermenter
Distillation
Water
Ethanol
Cyclone
Char
Hybrid thermochemical/biochemical biorefinery: Bio-oil fermentation
Bio-oil fermentation: Advantages & challenges
• Advantages – Densifies biomass for transportation – Leap frogs the problem of carbohydrate
depolymerization
• Challenges– Pyrolysis produces some fermentation
inhibitors – Gas, charcoal, and lignin do not contribute
to synfuels production– Limited development to date
Questions?
